Among the various video display systems available in the art, an optical projection system is known to be capable of providing a high quality video display in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors such that each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIG. 1, there is shown a cross sectional view of an array of M.times.N electrodisplacive actuated mirrors 100 disclosed in a copending, commonly owned application, U.S. Ser. No. 08/239,891, entitled "PIEZOELECTRIC ACTUATOR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF", wherein M and N are integers, comprising an active matrix 1, an array 4 of M.times.N actuators, e.g., 40, 40', 40", a corresponding array 7 of M.times.N mirrors, e.g., 70, 70', 70"and a corresponding array 9 of M.times.N connecting terminals, e.g., 90, 90', 90". Each of the actuators, e.g., 40, in turn, is provided with a top surface 46, a bottom surface 47, and a pair of external sides 48a, 48b; and has a bimorph structure, comprising a pair of electrodisplacive members 42a, 42b, a common signal electrode 43 located between the pair of electrodisplacive members 42a, 42b and a pair of reference electrodes 44a, 44b on the pair of external sides 48a, 48b of the actuator 40, respectively (as all of the actuators, e.g., 40, 40', 40", are essentially identical, the following description will be given with respect to a representative actuator 40).
The electrodisplacive members 42a, 42b are comprised of an electrodisplacive material such as a piezoelectric material, e.g., lead zirconium titanate (PZT), or an electrostrictive material, e.g., lead magnesium niobate-lead titanate(PMN-PT).
The bottom surface 47 of the actuator 40 is mounted on the active matrix 1; and a mirror 70 is mounted on the top surface 46 of the actuator 40. Further, a connecting terminal 90 is used for electrically connecting the common signal electrode 43 in the actuator 40 to the active matrix 1.
When a voltage is applied between the common signal electrode 43 and the reference electrodes 44a, 44b, the electrodisplacive material located therebetween will deform in a direction determined by the polarity of the voltage.
In a copending, commonly owned application, U.S. Ser. No. 08/216,754, entitled "ACTUATOR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF", there is disclosed a method for manufacturing such an array of M.times.N electrodisplacive actuators for use in the above-described optical projection system, the method comprising the steps of:
(1) forming a multilayered ceramic structure having M layers of a first conductive metallization and M+1 layers of an electrodisplacive material, wherein each layer of the first conductive metallization is placed between two layers of the electrodisplacive material; PA1 (2) obtaining a composite ceramic wafer by slicing the multilayered ceramic structure in a direction normal to the layers of the first conductive metallization; PA1 (3) providing a plurality of regularly spaced horizontally directional trenches running parallel to each other using mechanical means, e.g., sawing, wherein each of the trenches is located at an equidistance from two adjacent layers of the first conductive metallization; PA1 (4) depositing a second conductive metallization; and PA1 (5) preparing N-1 regularly spaced vertically directional cuts on the composite ceramic wafer prepared using steps(3) and (4) to thereby obtain the array of M.times.N electrodisplacive actuators. PA1 (a) preparing a ceramic wafer, made of an electrostrictive material, having a top and a bottom surfaces; PA1 (b) forming an array of M.times.N regularly spaced, identically sized first electrodes on the bottom surface of said ceramic wafer and a set of 2.times.(M+1) identically sized second electrodes on the top surface thereof, wherein each of the 2.times.(M+1) second electrodes, having a pair of side edges running parallel to each other and to the vertical direction, extends vertically across the top surface, and each of the M.times.N first electrodes, when projected onto the top surface, includes two adjacent second electrodes and the centerline thereof coincides with the centerline therebetween; PA1 (c) mounting said ceramic wafer treated in accordance with said step (b) on an active matrix, including a substrate, an array of M.times.N transistors and an array of M.times.N connecting terminals to thereby connect each of the first electrodes with each of the M.times.N connecting terminals; PA1 (d) covering the top surface of said ceramic wafer, including the 2.times.(M+1) second electrodes, treated in accordance with said steps (b) and (c) with an insulating layer; PA1 (e) providing a set of (M+1) photoresistive necked segments on top of the insulating layer covering the top surface of said ceramic wafer, including the 2.times.(M+1) second electrodes, each of the photoresistive necked segments, extending in the vertical direction, is placed on a portion of the insulating layer covering a pair of second electrode, wherein the pair of second electrodes, when projected onto the bottom surface, is made up of two neighboring second electrodes from two horizontally adjacent first electrodes; PA1 (f) forming a set of M trenches, wherein each of the M trenches, provided with a pair of side surfaces and a bottom surface, is located between two adjacent second electrodes, the centerline thereof coinciding with the centerline of each of the first electrodes on the same column and the centerline between the two adjacent second electrodes, runs parallel to the second electrodes, and is further provided with a set of N-1 grooves, running perpendicular thereto; PA1 (g) removing the photoresistive necked segments; PA1 (h) placing an array of M.times.N hinges on the top surface of said ceramic wafer treated in accordance with said steps (b), (c), (d), (e), (f) and (g), wherein each of the M.times.N hinges is provided with a top surface and a bottom surface provided with a protrusion mounted simultaneously on the insulating layers covering the two adjacent second electrodes separated by a trench therebetween; PA1 (i) forming a mirror on the top surface of each of the M.times.N hinges; and PA1 (j) making appropriate electrical connections to thereby form an array of M.times.N electrodisplacive actuated mirrors. PA1 an active matrix including a substrate, an array of M.times.N transistors and an array of M.times.N connecting terminals thereon; PA1 an array of M.times.N hinges, wherein each of the M.times.N hinges is provided with a flat top surface and a bottom surface having a protrusion mounted on the top of each of the M.times.N electrodisplacive actuators; PA1 an array of M.times.N connecting terminals, wherein each of the connecting terminals is used for electrically connecting each of the first electrodes with the active matrix; and PA1 an array of M.times.N mirrors, wherein each of the M.times.N mirrors is mounted on the top surface of each of the M.times.N hinges.
The first and the second conductive metallizations serve as the common signal electrode, e.g., 43, and the reference electrodes, e.g., 44a, 44b, in the completed actuated mirror array, respectively.
There is a number of problems associated with the above-described methods for manufacturing an array of M.times.N electrodisplacive actuators, however. First of all, the first conductive metallization, which will serve as the common signal electrode 43 in the completed actuated mirror array, may be deformed or bend during the sintering process involved in the preparation of the multilayered ceramic structure, which may, in turn, make it difficult to form dimensionally correct trenches and, hence, the actuators. Another problem present in the above method is that, for the first conductive metallization, it requires expensive electrode materials having high melting points such as platinum (Pt) or palladium (Pd) so as for the first conductive metallization to withstand an extremely high sintering temperature, e.g., 1,250.degree. C. or higher. Since the array of M.times.N electrodisplacive actuators is manufactured using mechanical means, e.g., sawing, it may be difficult to obtain the desired reproducibility, reliability and yield in the manufacturing of the M.times.N electrodisplacive actuated mirrors; and, furthermore, there may be a limit to the down sizing thereof.